Both rocket moor design and propellant design are aided by detailed in-situ information on the deflagration behavior of propellant surfaces present understanding of the details of propellant combustion is however, sparse. More must be learned about localized, transient burning rates, their dependence on grain and binder composition and grain size distribution, and the coupling or regression rates of the various constituents in the grain.
Solid propellants generally have a granular, heterogeneous composition. The particle sizes of the various constituents generally range from 2 to 1000 microns, the largest being oxidizers. Consequently, local variations in transient burning rates of these constituents are expected. A spiked behavior in the local burning rate is known to occur in many propellants. During test burns in a combustion chamber, these local transients can couple to the acoustic field in the chamber, causing oscillation of the burning rate, further acoustically driving instabilities in the chamber.
High-speed photographic recording of a propellant burn in a combustion chamber is considered to be a valuable tool both for propellant formulation and for motor design. Much of the present knowledge of propellant deflagration has been garnered by high-speed photoqraphy.
Because of the need and/or desire for magnification of the image, the depth of field of such high-speed cinematography can be very limited. If the position of the propellant grain or strand is fixed during a burn sequence, the number of in-focus frames is limited by the limited depth-of-field. This drawback can be overcome, at least in part, by employing a servopositioner to advance the burning propellant to maintain the desired burning surface within the limited depth-of-field of the recording apparatus.
Solid rocket propellant has a tendency to burn along all exposed surfaces, a phenomenon known as flashing. Consequently, a strand forms a pointed surface during deflagration. Because of the limitations in photographic equipment, the desired burning surface is a flat plane. Preferably parallel to the film plane and at an angle with respect to the length of the strand. Several methods have been employed to inhibit flashing. One method, commonly used, is simply to briefly soak the strand in water immediately prior to deflagration. However, if the water is applied more than a few minutes before deflagration, its ability to inhibit flashing is greatly reduced. Therefore water cannot be used for any runs where the propellant must be prepared much in advance of deflagration. Silicone grease has been employed as an inhibitor but it does not fully prevent the sides of the strand from burning. The silicone grease also releases considerable smoke during deflagration, thereby interfering with photographic recording.
Accordingly it is an object of the present invention to provide a method for inhibiting burning on at least a portion of the exposed surface of a specimen of solid rocket propellant during deflagration.
Other objects and aspects of this invention will be apparent to those skilled in the art.